Many machining operations are directed to removing material from a workpiece in a controlled manner. “High precision” machining generally refers to techniques for cutting, grinding, and other forms of workpiece modification where tolerances can be relatively tightly controlled. Many parts used in modern machine systems need to have a relatively exact size, configuration, alignment of features or factors such as surface finish to function properly in a service environment. Engineers have long sought machining methods with improved precision for manufacturing new parts. In recent years, increasing attention has been paid to the use of high precision machining techniques in the growing field of remanufacturing.
Remanufacturing of machine components has provided new opportunities for revenue and resource conservation. New techniques enabling the reuse of previously scrapped parts have also been developed. A common technique for remanufacturing machine components such as hydraulic valve parts involves removing wear and/or repairing damage to the parts, often by grinding. It is generally desirable to return the parts to specifications as close to the original specifications as practicable. Many hydraulic valve parts, notably those used in fuel injection systems, are originally machined at relatively tight tolerances. Valve members, for example, may be required to actuate quite rapidly and precisely many times during a service life. To enable salvaged valve members to operate similarly when returned to service, tolerances in remanufacturing often need to be at least as tight as tolerances in original manufacturing. An added incentive to tightly controlling tolerances in remanufacturing is the possibility of returning parts to service with the same or identical components to those with which they were previously used.
U.S. Pat. No. 5,893,793 to Nishio et al. (“Nishio”) is directed to machining an elongated cylindrical article of ceramic material. In Nishio, an article to be machined such as an engine valve is chucked at opposite longitudinal end portions of the article, then driven by one of the chucks at one end while allowing slip in the chuck at the other end. Positional deviation between a center axis passing between the chucks and an axis of the article is purportedly removed by a self-aligning centrifugal action of the article. The article is then securely chucked, and machined with a machining tool. The strategy is stated to improve grinding accuracy. Nishio states that at least one of the chuck heads is made of a material softer than a ceramic material of the workpiece. This enables the workpiece to wear the slipping chuck head to remove any positional deviation between the axes. While Nishio appears to improve grinding accuracy for certain articles, other components are not amenable to machining with Nishio's highly specialized techniques.